1. Field of the Invention
The present invention relates to an exposing device and an image forming apparatus, and more particularly, to an exposing device (printer head) to be used for an electrophotographic copier, printer, facsimile, and the like, and to an image forming apparatus including the exposing device.
2. Description of the Related Art
Hitherto, an image forming apparatus using an electrophotographic method has been known, which includes an exposing device (printer head) arranged above a circumferential surface of a photosensitive drum that is a member to be exposed with light. A light emitting element array of LEDs or the like is provided in the printer head.
FIG. 11 is a schematic diagram of a related art image forming apparatus 1000 disclosed in Japanese Patent Application Laid-Open No. 2004-098289.
The image forming apparatus 1000 includes a photosensitive drum 1010 and a printer head (optical writing head) 1020 arranged facing the photosensitive drum 1010.
Light output from multiple LEDs (light source) 1030 arranged in the printer head 1020 is caused to pass through an erecting equal magnification imaging system such as a rod lens array and imaged on the photosensitive drum 1010, thus exposing the photosensitive drum 1010 with light.
The rod lens array includes a large number of lens elements 1040 arranged in an array and configured to perform the erecting equal magnification imaging so that the light output from the multiple LEDs 1030 is imaged on the photosensitive drum 1010.
In the optical writing head 1020 of the related art image forming apparatus 1000, the light source 1030 that does not have a spatial coherence, such as an LED, is used.
In general, a divergence angle of light emitted from a light source that does not have the spatial coherence is wide, and hence the light emitted from a single light source 1030 is input to multiple optical systems for forming a spot.
For this reason, in order to guide the light from the light source 1030 to the photosensitive drum 1010, the erecting equal magnification imaging system such as the rod lens array (lens elements 1040) has been used as an optical system. However, the light entering a gap of the rod lens array (lens elements 1040) is not guided to the photosensitive drum 1010, and hence the usage efficiency of the light is not sufficient.
Further, when the printer head 1020 and the photosensitive drum 1010 are arranged close to each other to increase the usage efficiency of the light, a focal depth of the erecting equal magnification imaging system becomes small, causing a problem in that imaging property of the erecting equal magnification imaging system is changed due to a misalignment caused by a vibration or the like of the photosensitive drum 1010.